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       strerror, strerror_r, strerror_l - return string describing error number


       #include <string.h>

       char *strerror(int errnum);

       int strerror_r(int errnum, char *buf, size_t buflen);
                   /* XSI-compliant */

       char *strerror_r(int errnum, char *buf, size_t buflen);
                   /* GNU-specific */

       char *strerror_l(int errnum, locale_t locale);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

           The XSI-compliant version is provided if:
           (_POSIX_C_SOURCE >= 200112L) && !  _GNU_SOURCE
           Otherwise, the GNU-specific version is provided.


       The strerror() function returns a pointer to a string that describes the error code passed
       in the argument errnum, possibly using the LC_MESSAGES  part  of  the  current  locale  to
       select  the  appropriate  language.   (For  example,  if  errnum  is  EINVAL, the returned
       description will be "Invalid  argument".)   This  string  must  not  be  modified  by  the
       application,  but  may be modified by a subsequent call to strerror() or strerror_l().  No
       other library function, including perror(3), will modify this string.

       The strerror_r() function is similar to strerror(), but is thread safe.  This function  is
       available  in  two versions: an XSI-compliant version specified in POSIX.1-2001 (available
       since glibc 2.3.4, but not POSIX-compliant until glibc 2.13), and a  GNU-specific  version
       (available  since glibc 2.0).  The XSI-compliant version is provided with the feature test
       macros settings shown in the SYNOPSIS; otherwise the GNU-specific version is provided.  If
       no  feature  test macros are explicitly defined, then (since glibc 2.4) _POSIX_C_SOURCE is
       defined by  default  with  the  value  200112L,  so  that  the  XSI-compliant  version  of
       strerror_r() is provided by default.

       The  XSI-compliant  strerror_r()  is  preferred for portable applications.  It returns the
       error string in the user-supplied buffer buf of length buflen.

       The GNU-specific strerror_r() returns a pointer to a string containing the error  message.
       This  may be either a pointer to a string that the function stores in buf, or a pointer to
       some (immutable) static string (in which case buf is unused).  If the  function  stores  a
       string in buf, then at most buflen bytes are stored (the string may be truncated if buflen
       is too small and errnum is unknown).  The string always includes a terminating  null  byte

       strerror_l()  is  like  strerror(), but maps errnum to a locale-dependent error message in
       the locale specified by locale.  The behavior of strerror_l() is undefined  if  locale  is
       the special locale object LC_GLOBAL_LOCALE or is not a valid locale object handle.


       The  strerror(),  strerror_l(),  and  the  GNU-specific  strerror_r() functions return the
       appropriate error description string, or an "Unknown  error  nnn"  message  if  the  error
       number is unknown.

       The  XSI-compliant  strerror_r()  function  returns  0 on success.  On error, a (positive)
       error number is returned (since glibc 2.13), or  -1  is  returned  and  errno  is  set  to
       indicate the error (glibc versions before 2.13).

       POSIX.1-2001 and POSIX.1-2008 require that a successful call to strerror() or strerror_l()
       shall leave errno unchanged, and note that, since no function return value is reserved  to
       indicate  an error, an application that wishes to check for errors should initialize errno
       to zero before the call, and then check errno after the call.


       EINVAL The value of errnum is not a valid error number.

       ERANGE Insufficient storage was supplied to contain the error description string.


       The strerror_l() function first appeared in glibc 2.6.


       For an explanation of the terms used in this section, see attributes(7).

       │InterfaceAttributeValue                   │
       │strerror()     │ Thread safety │ MT-Unsafe race:strerror │
       │strerror_r(),  │ Thread safety │ MT-Safe                 │
       │strerror_l()   │               │                         │


       strerror() is specified by POSIX.1-2001, POSIX.1-2008,  C89,  and  C99.   strerror_r()  is
       specified by POSIX.1-2001 and POSIX.1-2008.

       strerror_l() is specified in POSIX.1-2008.

       The GNU-specific strerror_r() function is a nonstandard extension.

       POSIX.1-2001 permits strerror() to set errno if the call encounters an error, but does not
       specify what value should be returned as the function result in the event of an error.  On
       some  systems,  strerror() returns NULL if the error number is unknown.  On other systems,
       strerror() returns a string something like "Error nnn occurred" and sets errno  to  EINVAL
       if  the error number is unknown.  C99 and POSIX.1-2008 require the return value to be non-


       The GNU C Library uses a buffer of 1024  characters  for  strerror().   This  buffer  size
       therefore  should  be  sufficient  to  avoid an ERANGE error when calling strerror_r() and


       err(3), errno(3), error(3), perror(3), strsignal(3), locale(7)


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                                            2017-09-15                                STRERROR(3)